ABSTRACT
52The mechanisms by which surfactants affect spray atomization from a hydraulic nozzle and the retention of spray droplets on foliage are reviewed in this chapter and the potential importance of dynamic surface tension is highlighted. Using a laboratory microsprayer to generate monosize droplets from aqueous methanol at a constant velocity, we found a sigmoidal relationship between retention on pea leaves and surface tension, in confirmation of previous studies. Addition of surfactant above the critical micelle concentration (CMC) improved retention of the spray, suggesting that dynamic surface tension was important.
Solutions of different surfactant types and concentrations were applied to pea plants through a hydraulic nozzle mounted on a track sprayer. Foliar retention was found to be related to dynamic but not to equilibrium surface tension properties of the solutions. Surfactants decrease in-flight droplet size in hydraulic nozzle sprays and the effect of this on spray retention could be predicted by using a simple model of the retention process.
With the nonionic surfactants tested, retention depended more on concentration (w/v) than on chemical structure. Certain differences in results between the laboratory microsprayer and track sprayer were attributed mainly to the wide range of droplet size and velocity resulting from the latter.
